The problem of disposing of bulky waste materials is receiving increasing attention as existing landfills reach capacity and the availability of additional land for waste disposal decreases. Reducing waste, such as tires, in size permits volume densification and reduces the requirements of subsequent processing.
Machines which utilize paired shearing wheels to shred waste material into smaller pieces have been developed. For example, U.S. Pat. Nos. 4,901,929 and 4,607,800 to Barclay disclose machines in which counter-rotating shearing wheels overlap at the edges of shear members on the wheels to cut into the waste material like giant knives. Other patents teaching this type of machine include U.S. Pat. No. 4,374,573 to Rouse et al. and U.S. Pat. No. 3,931,935 to Holman. The Barclay, Rouse et al. and Holman machines are "primary" shredders in the sense that whole tires may be fed into the machines for shredding. As best seen in the above-cited U.S. Pat. No. 4,901,929 to Barclay, annular hubs are attached to the outside diameter of drive shafts and the shear members are fixed to the hubs. The term "shredder" as used herein means a machine which reduces objects by shearing action.
A second type of primary shredder is described in U.S. Pat. Nos. 3,991,944 and 4,241,882 to Baikoff. The Baikoff patents teach comminuting machines having counter-rotating shafts with comminutor rings. The rings include cutter-noses which come in close proximity to the outer diameter of the opposite shaft to which the rings are attached so as to provide the cutting action. The patents teach that the outer surfaces of the counter-rotating shafts act as anvils for the cutting action of the cutter-noses of the rings. The rings are attached to annular shaft-collars which extend from the outside diameter of the shafts. Thus, the shaft-collars are the functional equivalents of the shaft hubs of the other patents cited above.
While the primary waste-reducing machines of the prior art significantly reduce the size of tires and the like, in some applications it is desirable to provide further reduction. One method is to first freeze and then jolt the material to shatter the material. However, this can be an expensive method.
Wear of the shearing wheels is also an important concern. The clearance between overlapping adjacent edges of the shear members of the two shearing wheels must remain within a relatively small range for the shredder to operate effectively. The shear members therefore must be periodically replaced or resharpened. The above-cited patent to Rouse et al. teaches attaching resharpenable segments along the periphery of each shear member. However, resharpening requires removal of material along the overlapping adjacent edges, so that the clearance between edges is affected, as is the effectiveness of shredder. Consequently, the segments must be replaced regularly. The Barclay ('929) patent teaches a shear member having an overlapping radially outward end that is comprised of a center annular member extending from a hub and sandwiched between two resharpenable tool members. As a tool member is resharpened, a shim is placed between the center annular member and each tool member to maintain the clearance between adjacent shear members. The problem with this assembly is that the center annular members must have a sufficiently wide axial width to withstand the stresses encountered during the arduous task of shearing tires and the like. As a result, the minimum center-to-center pitch of the shear members is relatively large and the resulting reduction in size may not be sufficient for certain applications.
It is an object of the present invention to provide a shearing machine which has a fine pitch of resharpenable shearing members and which allows a greater number of shears without rendering the machine more susceptible to breakage resulting from the increased torque necessary to achieve the increase in shears. Another object is to provide such a machine which can be used as either a primary or secondary shearing machine.